Intra-Articular Injectable Biomaterials for Cartilage Repair and Regeneration

Osteoarthritis is a degenerative joint disease characterized by cartilage deterioration and subsequent inflammatory changes in the underlying bone. Injectable hydrogels have emerged as a promising approach for controlled drug delivery in cartilage therapies. This review focuses on the latest developments in utilizing injectable hydrogels as vehicles for targeted drug delivery to promote cartilage repair and regeneration. The pathogenesis of osteoarthritis is discussed to provide a comprehensive understanding of the disease progression. Subsequently, the various types of injectable hydrogels used for intra-articular delivery are discussed. Specifically, physically and chemically crosslinked injectable hydrogels are critically analyzed, with an emphasis on their fabrication strategies and their capacity to encapsulate and release therapeutic agents in a controlled manner. Furthermore, the potential of incorporating growth factors, anti-inflammatory drugs, and cells within these injectable hydrogels are discussed. Overall, this review offers a comprehensive guide to navigating the landscape of hydrogel-based therapeutics in osteoarthritis.

Injectable, shear-thinning, photocrosslinkable, and tissue-adhesive hydrogels composed of diazirine-modified hyaluronan and dendritic polyethyleneimine

In the present study, we report the first synthesis of diazirine-modified hyaluronic acid (HA-DAZ). In addition, we also produced a precursor polymer solution composed of HA-DAZ and dendritic polyethyleneimine (DPI) that showed strong shear-thinning properties. Furthermore, its viscosity was strongly reduced (i.e., from 5 × 105 mPa s at 10-3 s-1 to 6 × 101 mPa s at 103 s-1), substantially, which enhanced solution injectability using a 21 G needle. After ultraviolet irradiation at 365 nm and 6 mW cm-2, the HA-DAZ/DPI solution achieved rapid gelation, as measured using the stirring method, and its gelation time decreased from 200 s to 9 s as the total concentrations of HA-DAZ and DPI increased. Following UV irradiation, the storage modulus increased from 40 to 200 Pa. In addition, reversible sol-gel transition and self-healing properties were observed even after UV irradiation. This suggests that the HA-DAZ/DPI hydrogel was crosslinked in multiple ways, i.e., via covalent bonding between the diazirine and amine groups and via intermolecular interactions, including hydrogen bonding, electrostatic interactions, and hydrophobic interactions. A lap shear test showed that the HA-DAZ/DPI hydrogel exhibited strong adhesiveness as a fibrin glue following UV irradiation. Finally, the HA-DAZ/DPI hydrogel showed higher tissue reinforcement than fibrin glue in an ex vivo burst pressure test of the porcine esophageal mucosa.

Sulfonium-Cross-Linked Hyaluronic Acid-Based Self-Healing Hydrogel: Stimuli-Responsive Drug Carrier with Inherent Antibacterial Activity to Counteract Antibiotic-Resistant Bacteria

Augmentation of the activity of Food and Drug Administration-approved antibiotics by an adjuvant or antibiotic carrier is considered one of the promising strategies to fight against antibiotic-resistant bacteria. This study reports the development of sulfonium-cross-linked hyaluronic acid (HA)-based polymer (HA-SS-HA) as an inherent antimicrobial agent and antibiotic carrier. The HA-SS-HA polymer offers the potential for encapsulating various classes of antibiotics and accomplishing a stimuli-responsive release profile in the presence of hyaluronidase produced by bacterial cells within their extracellular environment. Systematic antibacterial studies reveal that the HA-SS-HA-encapsulated antibiotics (vancomycin, amoxicillin, and tetracycline) restore its activity against the antibiotic-resistant bacterial cells methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE), and Pseudomonas aeruginosa. The HA-SS-HA gel shows robust efficacy in eradicating the mature biofilm of Staphylococcus aureus (S. aureus). The membrane-disrupting activity reveals that HA-SS-HA can also counteract the antibiotic resistance mechanism of the bacterial cells. The in vivo studies reveal excellent wound-healing activity of HA-SS-HA in albino laboratory-bred (BALB/c) mice. The outcome of additional antibacterial studies reveals that antibiotics-encapsulated HA-SS-HA hydrogel can effectively combat Gram-negative, Gram-positive, and antibiotic-resistant bacterial strains. Therefore, revitalizing the activity of commercial antibiotics by HA-SS-HA can be considered a valuable and economically effective strategy to fight against antibiotic-resistant bacteria.

Bioadhesive and Injectable Hydrogels and Their Correlation with Mesenchymal Stem Cells Differentiation for Cartilage Repair: A Mini-Review

Injectable bioadhesive hydrogels, known for their capacity to carry substances and adaptability in processing, offer great potential across various biomedical applications. They are especially promising in minimally invasive stem cell-based therapies for treating cartilage damage. This approach harnesses readily available mesenchymal stem cells (MSCs) to differentiate into chondrocytes for cartilage regeneration. In this review, we investigate the relationship between bioadhesion and MSC differentiation. We summarize the fundamental principles of bioadhesion and discuss recent trends in bioadhesive hydrogels. Furthermore, we highlight their specific applications in conjunction with stem cells, particularly in the context of cartilage repair. The review also encompasses a discussion on testing methods for bioadhesive hydrogels and direct techniques for differentiating MSCs into hyaline cartilage chondrocytes. These approaches are explored within both clinical and laboratory settings, including the use of genetic tools. While this review offers valuable insights into the interconnected aspects of these topics, it underscores the need for further research to fully grasp the complexities of their relationship.

Microstructure-united heterogeneous sodium alginate doped injectable hydrogel for stable hemostasis in dynamic mechanical environments

Injectable hydrogels that can withstand compressive and tensile forces hold great promise for preventing rebleeding in dynamic mechanical environments after emergency hemostasis of wounds. However, current injectable hydrogels often lack sufficient compressive or tensile performance. Here, a microstructure-united heterogeneous injectable hydrogel (MH) was constructed. The heterogeneous structure endowed MH with a unique "microstructures consecutive transmission" feature, which allowed it to exhibit high compressive and tensile performance simultaneously. In this work, two types of sodium alginate doped hydrogels with different microstructures were physically smashed into microgels, respectively. By mixing the microgels, MH with one micro-pores featured microstructure and another nano-pores featured microstructure can be formed. The obtained MH can withstand both compressive and tensile forces and showed high mechanical performance (compressive modulus: 345.67 ± 10.12 kPa and tensile modulus: 245.19 ± 7.82 kPa). Furtherly, MH was proven to provide stable and sustained hemostasis in the dynamic mechanical environment. Overall, this work provided an effective strategy for constructing injectable hydrogel with high compressive and tensile performance for hemostasis in dynamic mechanical environments.

Microenvironment responsive nanocomposite hydrogel with NIR photothermal therapy, vascularization and anti-inflammation for diabetic infected wound healing

Bacterial infection, excessive inflammation and damaging blood vessels network are the major factors to delay the healing of diabetic ulcer. At present, most of wound repair materials are passive and can't response to the wound microenvironment, resulting in a low utilization of bioactive substances and hence a poor therapeutic effect. Therefore, it's essential to design an intelligent wound dressing responsive to the wound microenvironment to achieve the release of drugs on-demand on the basis of multifunctionality. In this work, metformin-laden CuPDA NPs composite hydrogel (Met@ CuPDA NPs/HG) was fabricated by dynamic phenylborate bonding of gelatin modified by dopamine (Gel-DA), Cu-loaded polydopamine nanoparticles (CuPDA NPs) with hyaluronic acid modified by phenyl boronate acid (HA-PBA), which possessed good injectability, self-healing, adhesive and DPPH scavenging performance. The slow release of metformin was achieved by the interaction with CuPDA NPs, boric groups (B-N coordination) and the constraint of hydrogel network. Metformin had a pH and glucose responsive release behavior to treat different wound microenvironment intelligently. Moreover, CuPDA NPs endowed the hydrogel excellent photothermal responsiveness to kill bacteria of >95% within 10 min and also the slow release of Cu²⁺ to protect wound from infection for a long time. Met@ CuPDA NPs/HG also recruited cells to a certain direction and promoted vascularization by releasing Cu²⁺. More importantly, Met@CuPDA NPs/HG effectively decreased the inflammation by eliminating ROS and inhibiting the activation of NF-κB pathway. Animal experiments demonstrated that Met@CuPDA NPs/HG significantly promoted wound healing of diabetic SD rats by killing bacteria, inhibiting inflammation, improving angiogenesis and accelerating the deposition of ECM and collagen. Therefore, Met@CuPDA NPs/HG had a great application potential for diabetic wound healing.

Functionalization of hyaluronic acid for development of self-healing hydrogels for biomedical applications: A review

Materials that are capable of undergoing self-repair following any physical damage or rupture due to external stimuli are identified as self-healing materials. Such materials are engineered by crosslinking the polymer backbone chains typically through reversible linkages. These reversible linkages include imines, metal-ligand coordination, polyelectrolyte interaction, disulfide, etc. These bonds are reversibly responsive to changes in various stimuli. Newer self-healing materials are now being developed in the field of biomedicine. Chitosan, cellulose, starch etc. are a few examples of polysaccharides that are generally used to synthesize such materials. Hyaluronic acid has been a very recent addition to the list of polysaccharides that are being investigated for construction of self-healing materials. It is non-toxic, non-immunogenic, has good gelation property and good injectability. Hyaluronic acid based self-healing materials are particularly employed for targeted drug delivery, protein and cell delivery, electronics, biosensors and many such biomedical applications. This review critically focuses on the functionalization of hyaluronic acid to fabricate self-healing hydrogels for biomedical applications. It also explores and sums up the mechanical data as well as self-healing efficiency of the hydrogels across wide range of interactions as discussed in the review below.

Injectable and tissue adhesive EGCG-laden hyaluronic acid hydrogel depot for treating oxidative stress and inflammation

Oxidative stress and inflammation are common pathological mechanisms for the progression of tissue degeneration. Epigallocatechin-3-gallate (EGCG) features antioxidant and anti-inflammatory properties, which is a promising drug for the treatment of tissue degeneration. Herein, we utilize the phenylborate ester reaction of EGCG and phenylboronic acid (PBA) to fabricate an injectable and tissue adhesive EGCG-laden hydrogel depot (EGCG HYPOT), which can achieve anti-inflammatory and antioxidative effects via smart delivery of EGCG. Specifically, the phenylborate ester bonds, formed by EGCG and PBA-modified methacrylated hyaluronic acid (HAMA-PBA), endow EGCG HYPOT injectability, shape adaptation and efficient load of EGCG. After photo-crosslinking, EGCG HYPOT exhibits good mechanical properties, tissue adhesion and sustained acid-responsive release of EGCG. EGCG HYPOT can scavenge oxygen and nitrogen free radicals. Meanwhile, EGCG HYPOT can scavenge intracellular reactive oxygen species (ROS) and suppress the expression of pro-inflammatory factors. EGCG HYPOT may provide a new idea for alleviation of inflammatory disturbance.

Silica Hydrogels as Platform for Delivery of Hyaluronic Acid

Hyaluronic acid (HA) is chondroprotective and anti-inflammatory drug used clinically for treatment of inflammatory disorders (arthritis, skin diseases, bowel diseases, etc.). In addition, HA is a crucial ingredient in the cosmetic products used to eliminate the unpleasant consequences of inflammatory skin diseases. The main disadvantages that limit its use are its low mechanical properties and its rapid biodegradation. In this paper, silica hydrogels are considered as a promising matrix for HA to improve its properties. The hybrid HA-silica hydrogels were synthesized by the sol-gel method. Morphology of the hydrogels was investigated by optical microscopy and scanning electron microscopy methods. Taking into account their potential applications for topical and injectable delivery, much attention was paid to investigation of deformation properties of the hydrogels under shear, compression, and tension. Their resistance to enzymatic degradation in vitro was estimated. Kinetics and mechanisms of HA release from the hybrid hydrogels in vitro were also studied. It was found that the indicated properties can be controlled by synthesis conditions, HA molecular weight, and its loading in the hydrogels. Silica hydrogels are a prospective platform for the development of new soft formulations and cosmetic compositions of HA with improved pharmacological and consumer properties.

Designing functional hyaluronic acid-based hydrogels for cartilage tissue engineering

Damage to cartilage tissues is often difficult to repair owing to chronic inflammation and a lack of bioactive factors. Therefore, developing bioactive materials, such as hydrogels acting as extracellular matrix mimics, that can inhibit the inflammatory microenvironment and promote cartilage repair is crucial. Hyaluronic acid, which exists in cartilage and synovial fluid, has been extensively investigated for cartilage tissue engineering because of its promotion of cell adhesion and proliferation, regulation of inflammation, and enhancement of cartilage regeneration. However, hyaluronic acid-based hydrogels have poor degradation rates and unfavorable mechanical properties, limiting their application in cartilage tissue engineering. Recently, various multifunctional hyaluronic acid-based hydrogels, including alkenyl, aldehyde, thiolated, phenolized, hydrazide, and host–guest group-modified hydrogels, have been extensively studied for use in cartilage tissue engineering. In this review, we summarize the recent progress in the multifunctional design of hyaluronic acid-based hydrogels and their application in cartilage tissue engineering. Moreover, we outline the future research prospects and directions in cartilage tissue regeneration. This would provide theoretical guidance for developing hyaluronic acid-based hydrogels with specific properties to satisfy the requirements of cartilage tissue repair.

Recent Developments and Current Applications of Organic Nanomaterials in Cartilage Repair

Regeneration of cartilage is difficult due to the unique microstructure, unique multizone organization, and avascular nature of cartilage tissue. The development of nanomaterials and nanofabrication technologies holds great promise for the repair and regeneration of injured or degenerated cartilage tissue. Nanomaterials have structural components smaller than 100 nm in at least one dimension and exhibit unique properties due to their nanoscale structure and high specific surface area. The unique properties of nanomaterials include, but are not limited to, increased chemical reactivity, mechanical strength, degradability, and biocompatibility. As an emerging nanomaterial, organic nanocomposites can mimic natural cartilage in terms of microstructure, physicochemical, mechanical, and biological properties. The integration of organic nanomaterials is expected to develop scaffolds that better mimic the extracellular matrix (ECM) environment of cartilage to enhance scaffold-cell interactions and improve the functionality of engineered tissue constructs. Next-generation hydrogel technology and bioprinting can be used not only for healing cartilage injury areas but also for extensive osteoarthritic degenerative changes within the joint. Although more challenges need to be solved before they can be translated into full-fledged commercial products, nano-organic composites remain very promising candidates for the future development of cartilage tissue engineering.

Bioinspired Hydrogels as Platforms for Life-Science Applications: Challenges and Opportunities

Hydrogels, as interconnected networks (polymer mesh; physically, chemically, or dynamic crosslinked networks) incorporating a high amount of water, present structural characteristics similar to soft natural tissue. They enable the diffusion of different molecules (ions, drugs, and grow factors) and have the ability to take over the action of external factors. Their nature provides a wide variety of raw materials and inspiration for functional soft matter obtained by complex mechanisms and hierarchical self-assembly. Over the last decade, many studies focused on developing innovative and high-performance materials, with new or improved functions, by mimicking biological structures at different length scales. Hydrogels with natural or synthetic origin can be engineered as bulk materials, micro- or nanoparticles, patches, membranes, supramolecular pathways, bio-inks, etc. The specific features of hydrogels make them suitable for a wide variety of applications, including tissue engineering scaffolds (repair/regeneration), wound healing, drug delivery carriers, bio-inks, soft robotics, sensors, actuators, catalysis, food safety, and hygiene products. This review is focused on recent advances in the field of bioinspired hydrogels that can serve as platforms for life-science applications. A brief outlook on the actual trends and future directions is also presented.

Injectable Natural Polymer Hydrogels for Treatment of Knee Osteoarthritis

Osteoarthritis (OA) is a serious chronic and degenerative disease that increasingly occurs in the aged population. Its current clinical treatments are limited to symptom relief and cannot regenerate cartilage. Although a better understanding of OA pathophysiology has been facilitating the development of novel therapeutic regimen, delivery of therapeutics to target sites with minimal invasiveness, high retention, and minimal side effects remains a challenge. Biocompatible hydrogels have been recognized to be highly promising for controlled delivery and release of therapeutics and biologics for tissue repair. In this review, the current approaches and the challenges in OA treatment, and unique properties of injectable natural polymer hydrogels as delivery system to overcome the challenges are presented. The common methods for fabrication of injectable polysaccharide-based hydrogels and the effects of their composition and properties on the OA treatment are detailed. The strategies of the use of hydrogels for loading and release cargos are also covered. Finally, recent efforts on the development of injectable polysaccharide-based hydrogels for OA treatment are highlighted, and their current limitations are discussed.

Hydrogel, Electrospun and Composite Materials for Bone/Cartilage and Neural Tissue Engineering

Injuries of the bone/cartilage and central nervous system are still a serious socio-economic problem. They are an effect of diversified, difficult-to-access tissue structures as well as complex regeneration mechanisms. Currently, commercially available materials partially solve this problem, but they do not fulfill all of the bone/cartilage and neural tissue engineering requirements such as mechanical properties, biochemical cues or adequate biodegradation. There are still many things to do to provide complete restoration of injured tissues. Recent reports in bone/cartilage and neural tissue engineering give high hopes in designing scaffolds for complete tissue regeneration. This review thoroughly discusses the advantages and disadvantages of currently available commercial scaffolds and sheds new light on the designing of novel polymeric scaffolds composed of hydrogels, electrospun nanofibers, or hydrogels loaded with nano-additives.

Hyaluronic Acid Hydrogels Crosslinked in Physiological Conditions: Synthesis and Biomedical Applications

Hyaluronic acid (HA) hydrogels display a wide variety of biomedical applications ranging from tissue engineering to drug vehiculization and controlled release. To date, most of the commercially available hyaluronic acid hydrogel formulations are produced under conditions that are not compatible with physiological ones. This review compiles the currently used approaches for the development of hyaluronic acid hydrogels under physiological/mild conditions. These methods include dynamic covalent processes such as boronic ester and Schiff-base formation and click chemistry mediated reactions such as thiol chemistry processes, azide-alkyne, or Diels Alder cycloaddition. Thermoreversible gelation of HA hydrogels at physiological temperature is also discussed. Finally, the most outstanding biomedical applications are indicated for each of the HA hydrogel generation approaches.

Injectable poly(γ-glutamic acid)-based biodegradable hydrogels with tunable gelation rate and mechanical strength

Polypeptide-based hydrogels have potential applications in polymer therapeutics and regenerative medicine. However, designing reliable polypeptide-based hydrogels with a rapid injection time and controllable stiffness for clinical applications remains a challenge. Herein, a class of injectable poly(γ-glutamic acid) (PGA)-based hydrogels were constructed using furfurylamine and tyramine-modified PGA (PGA-Fa-Tyr) and the crosslinker dimaleimide poly(ethylene glycol) (MAL-PEG-MAL), through a facile strategy combining enzymatic crosslinking and Diels-Alder (DA) reaction. The injectable hydrogels could be quickly gelatinized and the gelation time, ranging from 10 to 95 s, could be controlled by varying the hydrogen peroxide (H2O2) concentration. Compared with hydrogels formed by single enzymatic crosslinking, the compressive stress and strain of the injectable hydrogels were remarkably enhanced because of the occurrence of the subsequent DA reaction in the hydrogels, suggesting the DA network imparted an outstanding toughening effect on the hydrogels. Furthermore, the mechanical strength, swelling ratio, pore size, and degradation behavior of the injectable hydrogels could be easily controlled by changing the molar ratios of H2O2/Tyr or furan/maleimide. More importantly, injectable hydrogels encapsulating bovine serum albumin exhibited sustained release behavior. Thus, the developed hydrogels hold great potential for applications in biomedical fields, such as tissue engineering and cell/drug delivery.

An Engineered Protein Adhesive with Properties of Tissue Integration and Controlled Release for Efficient Cartilage Repair

Cartilage damage is a prevalent health concern among humans. The inertness of cartilage, the absence of self-healing properties, and the lack of appropriate repair materials that integrate into the tissue pose a significant challenge for cartilage repair. Thus, it is important to develop novel soft biomaterials with strong tissue adhesion and chondrogenic capabilities for cartilage repair. Herein, a new type of protein adhesive is reported that exhibits superior cartilage repair performance. The material is fabricated by the electrostatic combination of chondroitin sulfate (CS) and positively charged elastin-like protein, which is derived from natural components of the extracellular matrix (ECM). The adhesive showed robust adhesion properties on different tissue substrates, offering a favorable environment for cartilage tissue integration. Noncovalent bonding between CS molecules in the glue allows for its controlled release, which is required for efficient chondrogenic differentiation. When implanted into a rat model of cartilage defect, this protein adhesive exhibited beneficial healing effects, as evidenced by enhanced chondrogenesis, sufficient ECM production, and lateral integration. Therefore, this engineered protein complex is a promising candidate for translational application in the field of cartilage repair.

Designing Hydrogels for 3D Cell Culture Using Dynamic Covalent Crosslinking

Designing simple biomaterials to replicate the biochemical and mechanical properties of tissues is an ongoing challenge in tissue engineering. For several decades, new biomaterials have been engineered using cytocompatible chemical reactions and spontaneous ligations via click chemistries to generate scaffolds and water swollen polymer networks, known as hydrogels, with tunable properties. However, most of these materials are static in nature, providing only macroscopic tunability of the scaffold mechanics, and do not reflect the dynamic environment of natural extracellular microenvironment. For more complex applications such as organoids or co-culture systems, there remain opportunities to investigate cells that locally remodel and change the physicochemical properties within the matrices. In this review, advanced biomaterials where dynamic covalent chemistry is used to produce stable 3D cell culture models and high-resolution constructs for both in vitro and in vivo applications, are discussed. The implications of dynamic covalent chemistry on viscoelastic properties of in vitro models are summarized, case studies in 3D cell culture are critically analyzed, and opportunities to further improve the performance of biomaterials for 3D tissue engineering are discussed.

Injectable DMEM-induced phenylboronic acid-modified hyaluronic acid self-crosslinking hydrogel for potential applications in tissue repair

Most of traditional injectable hydrogels based on light curing or enzyme crosslinking are difficult to control the crosslinking time accurately and lack tissue adhesion, which leads to difficult clinical application and poor tissue repair effect. In this study, a novel injectable DMEM (Dulbecco's Modified Eagle's Medium)-induced phenylboronic acid-modified hyaluronic acid self-crosslinking hydrogel was designed and prepared by combining the phenylboronic acid and a diol on hyaluronic acid as the main network, in which dynamically reversible phenylboronic acid esters imparted good self-healing properties and tissue adhesion properties to the hydrogels. Cell medium that induced the formation of the hydrogel could simulate the pH of the physiological environment and provide uniform nutrients for the encapsulated cells. In addition, in vitro cell experiments indicated that the DMEM-induced phenylboronic acid-modified hyaluronic acid self-crosslinking hydrogel was capable of supporting cell loading and proliferation, thus being a promising candidate for tissue repair materials.

Fabrication of Silk-Hyaluronan Composite as a Potential Scaffold for Tissue Repair

Interest is rapidly growing in the design and preparation of bioactive scaffolds, mimicking the biochemical composition and physical microstructure for tissue repair. In this study, a biomimetic biomaterial with nanofibrous architecture composed of silk fibroin and hyaluronic acid (HA) was prepared. Silk fibroin nanofiber was firstly assembled in water and then used as the nanostructural cue; after blending with hyaluronan (silk:HA = 10:1) and the process of freeze-drying, the resulting composite scaffolds exhibited a desirable 3D porous structure and specific nanofiber features. These scaffolds were very porous with the porosity up to 99%. The mean compressive modulus of silk-HA scaffolds with HA MW of 0.6, 1.6, and 2.6 × 10⁶ Da was about 28.3, 30.2, and 29.8 kPa, respectively, all these values were much higher than that of pure silk scaffold (27.5 kPa). This scaffold showed good biocompatibility with bone marrow mesenchymal stem cells, and it enhanced the cellular proliferation significantly when compared with the plain silk fibroin. Collectively, the silk-hyaluronan composite scaffold with a nanofibrous structure and good biocompatibility was successfully prepared, which deserved further exploration as a biomimetic platform for mesenchymal stem cell-based therapy for tissue repair.